Semiconductor wafer testing before dicing is a necessary and critical process step. Such testing provides early verification of circuit design and fabrication integrity. Typically, test probes are placed in contact with conductive pads of a device under test (DUT) to provide a test signal for such verification of the circuit, where the conductive pads are positioned on the surface of a wafer or DUT. These pads are known to have bump-like or convex shape, with the base of the pad incorporated into the wafer surface. A problem exists with a non-conductive layer of debris on the pad such as a non-conductive oxide layer impeding the conductive pad from receiving the test signal, where the debris is an artifact of the fabrication process. Currently, a scrubbing method is used to remove some of the non-conductive layer from the pads before applying the test signal. Many methods exist for removing the debris layer such as using the probe tip itself to scrub the pad while applying the test signal. For information about corresponding probe designs and scrub motion mechanics the reader is referred to U.S. Pat. No. 5,436,571 to Karasawa; U.S. Pat. Nos. 5,773,987 and 6,433,571 both to Montoya; U.S. Pat. No. 5,932,323 to Throssel and U.S. Appl. 2006/0082380 to Tanioka et al. Additional information about the probe-oxide semiconductor interface is found in U.S. Pat. No. 5,767,691 to Verkuil.
The scrub motion includes engaging a probe tip with a conductive pad, and applying an overdrive motion to the pad to cause the probe to scrub the layer of debris from the pad. Numerous problems arise from this method such as controlling the probe scrubbing action, managing undesirable debris accumulation on the probe tip, and the added need for a complicated and invasive probe cleaning processes to remove the debris from the probe tips. Consistent scrub control is of paramount importance. A probe is often too sensitive to the overdrive motion from the pad, causing a scrub depth that is too deep that not only removes a portion of the non-conductive layer, but also damages or breaches the conductive pad, thus rendering the wafer unusable. Debris accumulation on the probe tip degrades the electrical continuity between the probe and conductive pad, often times restricting the test signal and providing erroneous test results, where implementation of an undesirable test redundancy may then become necessary. Complicated probe tip cleaning methods, such as use of abrasion cleaning, have been used to remove debris from the probe tip by scouring. Such a technique not only disrupts the fabrication throughput, but also degrades the probe tip, resulting in shortened utility of the probes and requiring premature replacement.
Current attempts to address these issues have been met with shortcomings, where in one case a contact bump at the end of a probe has a nub made from rhodium nickel alloy fused to the contact bump. While such an alloy lends itself for creating a tip that is more robust for scrubbing, the need to disrupt fabrication throughput for a probe tip cleaning process still exists. Further, the geometry of the contact bump made from the alloy nub lends itself for undesirable accumulation of debris, thus necessitating relatively frequent cleaning. Another attempt has been implemented that includes a knife-like probe end in an effort to reduce debris accumulation for limiting the need for abrasive cleaning. Unfortunately, such geometry has been shown to lack scrubbing control and damage the pad due to the probe having a hyper-sensitivity to overdrive motion. For additional information about probe tip geometries the reader is referred to U.S. Pat. No. 6,633,176 and U.S. Appl. 2005/0189955 both to Takemoto et al., and U.S. Pat. No. 6,842,023 to Yoshida et al. employs contact probe whose tip tapers to a sloping blade or chisel.
It would be considered an advance in the art to provide a probe design having a probe tip with a self-cleaning skate that alleviates the need for using abrasion techniques to remove debris from the probe tip. A method of using a self-cleaning probe tip is needed that provides effective scrubbing for enabling testing. Further needed is a probe having a self-cleaning skate that is less sensitive to overdrive motion to enable consistent and predictable scrubbing for more reliable wafer testing and to alleviate the need for test redundancies.